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DAQ Back End Tutorial

DAQ Back End Tutorial. The players Data and flow control diagrams Brief description of each application Configuration and log files Starting and stopping applications Monitoring Status web page How to reach the experts Summary. The Players. This tutorial is about the

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DAQ Back End Tutorial

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  1. DAQ Back End Tutorial • The players • Data and flow control diagrams • Brief description of each application • Configuration and log files • Starting and stopping applications • Monitoring • Status web page • How to reach the experts • Summary

  2. The Players This tutorial is about the green guys

  3. C/R and DD • C/R = Collector/Router • Receives events from L3 nodes and SDAQ DMs • Routes an event according to the event’s stream(s): • Forwards calibration events to the CM • Forwards normal events to their DL(s) and as many as possible to the DD as well • Events w/o valid streams are dropped (with a warning) • Log file contains their event header dumps • Recently observed probability O(10-4), clustered in a few spikes • DD = (Data) Distributor • Receives events from the C/R(s) • Serves them to connected Examines according to each Examine’s stream and trigger wish lists

  4. The DL • DL = DataLogger • Receives events from C/R(s) • Saves them in files based on stream, run and partition (“{stream}_{run}_{partition}.raw”): • Each covers an integral number of luminosity blocks • Each has an associated event catalog file • Late events go to partition 000 • Events that arrive after their run has ended are dropped (with a warning) • Log file contains their event header dumps • Recently observed probability O(10-6), clustered in a few spikes • Is told by DLSAM when to move to the next disk

  5. SDAQ and DM • SDAQ = Secondary DAQ Supervisor • Controls IOC processes (“crates”) participating in SDAQ runs (calibration, monitoring, tests) • Starts and controls corresponding DM processes • DM = DataMerger • Receives SDAQ event fragments from IOC processes, merges them into complete events and sends those to a CR • Receives calibration and/or monitoring summaries from IOC processes and sends them to a CR, which will forward them to the CM • Currently this is the main use of the SDAQ

  6. The DSM • DSM = Data (Flow) State Manager • Controls all CR, DD and DL instances (“slaves”) on behalf of COOR • DD is non-vital  its replies are ignored • Puts any restarted “slave” into current DAQ state • Instructs CRs to which DL or CM to route a stream • Balances load over DLs • Currently there is only 1 DL • Supplies L3 and SDAQ Supervisors with weighted list of CRs • 2nd CR needed when > ~80 L3 nodes

  7. DLSAM and DLCAT • DLSAM = DL-SAM interface • Tells DL when to move to the next buffer disk • When occupancy or time limit is reached • Currently 2 TB available (30 disks) • Enough for 2 days of continuous (!) data taking at 12.5 MB/s • Uses SAM FSS to transfer completed files to Enstore • Checks PNFS before deleting any file • Lets DLCAT fix meta-data missing in the SAM DB • When the FSS lost its connection to the DB server • DLCAT = DL (event) Cataloguer • Checks and fixes meta-data missing in SAM DB • Stores and checks event catalogs in SAM DB • SAM DB (Oracle) will detect duplicate events, if any

  8. Configuration and Logs • /online/data/d0online/d0online_names.py • Shows on which host(s) an application runs • /online/data/datapath/$host/$app.setup • Configuration file for application $appon $host • $app can be collector, datalogger, distributor, dlcat, dlsam, dsm, sdaq • /online/log/$app/$year/$month • Holds formatted logfiles • /online/log/$app • Holds stdout/stderr files (out.* and stop.*)

  9. Starting and Stopping • Start an application • setup d0online • start_daq $app • Stop an application • First stop all ongoing runs! • Not needed for DLCAT (nor DLSAM, but see below) • setup d0online • stop_daq $app • DLSAM must run when the DL is recording a run • It instructs the DL when to move to the next disk

  10. Monitoring • Back end status web page • http://www-d0online.fnal.gov/www/daq/ operations/status/onlstatus-auto.html • Updated every minute • Frequently checked by the experts • Usually sufficient to verify the status or to discover problems

  11. Example Status Page Top Here the DSM reports all being OK for the ongoing run: Buffer disk subdirectory contents. DLSAM file state numbers are approximate.

  12. Example Status Page Bottom Here DLCAT is busy storing 3 event catalogs, another is waiting to be checked against the DB, and another has just arrived: The last 100 and 1000+ lines in an application’s log file, per host. Statistics for the last N files transferred. Trouble shooting hints.

  13. DSM Status Snapshot • Usually shows messages pertaining to the most recent COOR commands • Click on the DSM log file snapshot or episode link to see more details • Shows if the DSM is “ok” or “bad” • DSM is “ok” when all its required “slaves” are “ok” • The DD is not required • Click on the DSM status dump link to see more details • Compare the lists of required and connected slaves • Absent/misbehaving slaves can be (stopped and) restarted • First stop all ongoing runs

  14. DLSAM Status Snapshot • Shows status of buffer disks and files to be transferred • “timeout”  DL should move to another disk • Symptoms of SAM or Enstore problems: • Files staying “Queued” or “Submitted” > 1 hour • DLSAM may recover automatically • Stopping and restarting DLSAM rarely helps • The same applies to DLCAT • Files in “Alarm” state • Expert intervention needed

  15. How to reach the experts • The ODS D0 Online Support group has a primary: • Send e-mail to helpdesk@fnal.gov • Call the HelpDesk at x2345, or the Computing Services Operators at x2746 after hours, when the problem is urgent • In all cases mention the application that has problems (e.g. “dsm”) and its host (“d0olc” will do) • The HelpDesk/Operator needs that information to figure out whom to contact/page • Questions and comments about the DAQ Back End can be sent to: • d0online-support@fnal.gov

  16. Summary • The D0 DAQ back end is an integrated system comprising: • CR, DD, DL, DLCAT, DLSAM, DM, DSM, SDAQ • Their interactions/dependencies are not trivial • Contact the experts for configuration changes • DAQ shifters can stop and (re)start the applications • Following guidelines e.g. found in this tutorial • Please inform the experts of any problems • The status web page is handy for monitoring and trouble shooting

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